Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are particularly suitable for use in a broadcasting television camera, a cinema camera, a video camera, a digital still camera, and a silver-halide film camera.
Description of the Related Art
In recent years, as a zoom lens mounted on an image pickup apparatus such as a television camera, a cinema camera, a video camera, or a picture camera, a zoom lens having a wide angle of field and a high zoom ratio, being small in size and lightweight, and having high optical performance has been sought for. As the zoom lens having the wide angle of field and the high zoom ratio, there has been known a positive-lead type zoom lens including four or five lens units, in which a lens unit having a positive refractive power, which is configured not to move during zooming, is arranged closest to an object side as disclosed in Japanese Patent No. 3031598 and Japanese Patent No. 5049751, and as described in Japanese Patent Application Laid-Open No. 2005-292605.
In each of Japanese Patent No. 3031598 and Japanese Patent No. 5049751, a zoom lens including, in order from an object side to an image side, first to fifth lens units having positive, negative, positive, positive, and positive refractive powers, in which the first lens unit is used to perform focus adjustment, is disclosed.
In Japanese Patent Application Laid-Open No. 2005-292605, a zoom lens including, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power, in which a part of the fourth lens unit is used to perform focus adjustment, is described. In other words, in Japanese Patent Application Laid-Open No. 2005-292605, a zoom lens of a so-called rear focus type, in which a lens unit other than the first lens unit is used to perform the focus adjustment, is described.
In the above-mentioned positive-lead type zoom lens, in order to attain the wide angle of field, the high zoom ratio, reductions in size and weight, and the high optical performance, realizing both reductions in size and weight of the first lens unit, in particular, and suppression of aberration variations caused by the focus adjustment is a problem. In order to realize both the reductions and the suppression, it is important to appropriately set paraxial arrangements of the respective lens units, and to appropriately set which one of the lens units is used to perform the focus adjustment.
In the four-unit zoom lens for a television camera in the related art, in a case where the reductions in size and weight are to be attained while having the wide angle of field and the high zoom ratio, powers of the respective lens units need to be increased, which leads to a problem in that variations in various aberrations are disadvantageously increased during zooming and the focus adjustment.
In the case where the reductions in size and weight of the first lens unit are to be attained, in particular, there is a need to reduce the number of lenses of the first lens unit, or to increase the power of the first lens unit, and hence it has been difficult to suppress the variations in various aberrations caused by the zooming and the focus adjustment.
In Japanese Patent No. 3031598 and Japanese Patent No. 5049751, when zooming is performed from a wide angle end to a telephoto end, the paraxial arrangements and movement loci of the third lens unit and the fourth lens unit are defined to satisfactorily correct optical performance at an intermediate zoom position. However, a method in which a whole or a part of the first lens unit, which has a large lens diameter, is extended is adopted, and a focus lens unit includes a large number of lenses, with the result that the reductions in size and weight of the first lens unit are not attained.
On the other hand, in Japanese Patent Application Laid-Open No. 2005-292605, the rear focus type is adopted to attain the reductions in size and weight of the first lens unit. However, in a four- or five-unit zoom lens in which lens units on the image side of an aperture stop are configured not to move during zooming, which is often adopted in a broadcasting zoom lens, a focal length conversion optical system is generally arranged in a detachable state in an imaging lens unit, which is closest to the image side. Therefore, when the rear focus type is adopted, there is a problem in that an extension amount caused by the focus adjustment on a telephoto side and at an object distance on a close range side is disadvantageously increased when the focal length conversion optical system is attached.
It is an object of the present invention to provide a zoom lens having a wide angle of field, a high zoom ratio, and high optical performance over the entire zoom range, and being small in size and lightweight.